Process of carrying on catalytic reactions



Jan. 11 1927.

? F. A. CANON ET AL.

PROCESS OF CARRYING 0N CATALYTIC REACTIONS Filed June 20. 1922 zws - air oxidation-of naphthalene to Patented" a... '11, 1927.

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In the art of exothermic chemical reactions very practical difiiculties have been experienced in dissipating the excessive heat thereby. generated.

ljhe catalytic air oxidation of anthracene to anthraquinoneis an example of such a reaction. In that process the optimum temperature is above 450 0., lying roughly between 450 C. and 550 (1, but much higher temperatures will automatically build up unless prevented. Another example is the hthalic anhydride. In the latter process the optimum temperature is above 400 C., lying roughly between 400 C. and 450 (3., but much hlgher temperatures will also be reached unless prevented. L I

- Itis the object of the. present invention to provide an improved process for carrying out exothermicehemical reactions of this character which will permit the zone of reaction to reach and maintain a desired operating temperature, but will prevent its rise to an abnormal degree thereabove, the process being substantially automatic in operation. m

In processes of the above character in which the lower operating temperatures; obtain, water has been employed as a cooling agent, and in some respects has ideal characteristics. It is easily obtained, has great thermal capacity and can be conveniently directed and controlled. If properly brought into heat transferring relationship to the t-atalyst and the reaction vapors, it will be. caused to boil. This will result in-cthe absorption of great, quantities of heat from the catalyst and the reacting gases because of the large amount of heat (latent heat of vaporization) required to'etl'e'ct its boiling operation.

The use of mercury has been proposed but this material presents serious difficulties. In the first place its boiling point is too low for successful application without special though well-known methods of treatment which add-materially to the cost of operation. 'Itshigh cost makes unlimited use,

like that of water prohibitive. In addition it has a relatively low degree of heat absorption and a relatively low rate of heat conductivity. It is also subject to oxida'-' tion and its high specific gravity necessiconductivity and relatively light specific position can be obtaine W nrlssuro tates special and costly means for supporting and containing it.

In carrying out the present invention we have discovered that-if a composite metal,

consisting of one or more metals that will boil below the desired temperature of the reaction and one or more metals that will boil'above the said desired temperature of the reaction, isformed in proper propor-' tions, and this composite metal'is placed in heat-transferring relation to the catalyst and the reacting,gases, it will be caused to boil .at a temperature close to butslightly below. the desired temperature of the reaction and may be thus made to control the temperature of the reaction and keep the same well within maximum limits while permitting it to reach and maintain an eflicient minimum. In addition this composite metal will have a low melting point, great thermal capacity and gravity.

Taking the air oxidation process of converting' naphthalene to phthalic anhydride as an example of the practical application of the invention, aheated mixture of air or other oxygen containing gas and naphthalene inthe vapor phase and at a suitable temperature is brought into the presence of a suitable catalyst-for instance, vane; dium oxide. The naphthalene is thereby converted into phthalic anhydride and a large amount of heat is. thereby generated,

resulting in high temperatures unless controlled. The reaction temperature as above stated should run between 400 and 450- C. and the desired temperature \for the most effective working of this conversion process is ordinarily at approximately 425 C. Ob-

viously temperatures materially above the same are not only undesirable but expe: rience has demonstrated that very high temperature is detrimental to the product and apt to. be disastrous to the reaction ap'pa 1 ratus c If cadmium which boils at 778 C., and mercury which has a boiling point at 357 C. be mixed in certain proportions a com-' having a boilin point which is close to that of the desire reaction temperature, Thus a composition made up of 12%, b weight, of cadmium and 105 88% by weight 0 mercury, is semi-liqmd mately 425 C. is taken as satisfactory, a

boiling temperature of. about 400 C. for the controlling .composition is substantially satisfactory, and this can be obtained by a mixture of by weight .of cadmium and 75% by weight of mercury. This par' ticular mixture is. liquid at about 100 C. The composition has other valuable features besides that of its boiling point. While the thermal conductivity of mercury is relatively low (.0189) that of cadmium is .215, so that the thermalconductivity of the composition 3 tion to the Zone of reaction by any suitable is high, which' is an important factor that assists it in its heat-dissipating. qualities. Moreover the specific gravity of the composition is less than that, of mercury, the latter being13.5 while cadmium is 8.6.

In practicing-the process the composite metal is brought into heat transferring relaor obvious means, being held in a suitable container through; the walls of which the heat of reaction will pass to the metal, causing the latter to boil and thereby absorb such heat. The vapors thus generated may be collected, condensed and returned to heat transferring relationship to the zone of reaction for reuse, the low melting point of the metal making this easy of accomplishment.

Thus in the accompanying drawings: Figure 1 is a vertical sectional view diagrammatic in character of a type of apparatus for carrying out the process.

Figure 2 is a cross'sectional view of the same. 7

A chamber 3 containing a catalyst 4 is provided with an inlet 5, through which the preheated gases as above described are intro duced, and an outlet 5 from which the I treated gases pass for further treatment.

Inside this chamber is a container 6 in which the composite metal 7 is placed. The vapors from the boiling metal 7 rise to a condenser 8 which may be jacketed as shown at 9 to hold a cooling medium of lower boiling point, as for example, water.

The water may be made to boil in performing its condensing operation and the steam thus gen erated or the heat absorbed employed in turn for any useful purposes desired. The composition, however, having a low melting The same process may be successfully carried out in the catalytic oxidation of anthracene to anthraquinone. In that process anthracene in the vapor phase and mixed with air or other oxygen containing as in properly heated condition is broug l presence of a catalyst, for instance molybdenum oxide. The optimum temperature lies between 450 C. and 550 C. If, therefore, approximately 515 C. istaken as a desired working temperature, a composition of 60% by weight of cadmium and 40%- by weight of mercury will give a boiling point of about 492 C.

This process can thus be successfully carried out with the apparatus of the type as that above suggested for the production of phthalic anhydride and is of decided importance for the purpose of producing anthraquinone since so far as we are aware unsatisfactory catalytic oxidation process- .of this character. has been commercially practicable because of the difficulties of controlling the high temperatures necessary to the satisfactory working of the process with the materials used as controlling substances up to this time.

Having thus fully described our invention, what we claim now, and desire to secure by Letters Patent, is

it into the 1. The process of carrying on catalytic reactions which consists in carrying on an exothermic reactlon of a heated gas in the presence of a heated catalyst ranging approximately between 400 C. and.550 C. and maintaining such temperature by transmitting the excess heat exothermically generated to a composition of cadmium and mercury that will boil when said temperature is reached, and boiling said composition by said excess heat.

2. The process of converting anthracene to a'nthraquinone which consists in subjecting a mixture of anthracene vapor and an oxygen containing gas to a catalyst at a working temperature ranging approximately between 450 C. and 550 C. and maintaining said temperature by transmitting the excess heat generated to a composition of cadmium and mercury that will boil at said temperature.

p In testimony whereof, we afiix our signatures. v

FRANK A. CANON. CHESTER E. ANDREWS. 

